TDK conference 2016

Exertional myopathies in case of horses are common subjects of research. Rhabdomyolysis is a multifactorial problem, which usually happens after a longer period of rest followed by exercise. The main causes of the problem are assumed to be nutritional factors such as selen or vitamin E deficiency, electrolyte imbalances and genetic background that includes Polysaccharide storage myopathy (PSSM) and malignant hyperthermia (MH). Common sympthoms of the myopathies are muscle stiffness, swelling, pain and myoglobinuria. In Hargita region of Transylvania, in villages located relatively higher from sea level the prevalence of rhabdomyolysis is 17-23%, while in the neighboring villages located relatively lower, this rate is just about 2%. The purpose of my TDK research is to explore the genetic background of the noticed phenomenon.

We've created two groups for the research. In group “A” there were 20 horses from places located higher than 800 m, group “B” consisted of 10 randomly selected horses from areas located lower. The horses in both groups were fed by local hay, and in periods of hard work additional oats and barley. No additional vitamins, minerals or electrolytes were given. Hair samples were collected from 14 horses from group “A”, and 9 horses from group “B”, in order to perform the genetic analysis for GYS1 gene mutation responsible for PSSM type 1, and for RYR1 mutation causing MH. The samples were sent to the Animal Genetics Laboratory,UK.

The results of the genetic test were the following: from group “A” 7 horses were positive (heterozygotes) for GYS1 mutation, while the remaining 7 turned to be negative. For RYR1 mutation the whole group “A” was negative. In group “B” there was one positive heterozygote for GYS1, 9 horses were negative, while for RYR1 the whole group was negative. In the past 12 months 7 horses from group “A” and only 1 horse from group “B” had clinical manifestation of the disease. In group “A” 2 GYS1 positive horses did not show any clinical signs, while rhabdomyolysis occurred in two horses that tested negative for PSSM 1.

In general, based on our study it could be said that in case of horses that suffered from exertional rhabdomyolysis there was a higher prevalence of PSSM heterozygotes, than in individuals that were not affected by the problem. However, the myopathy occurred also in horses that presented negative results for both gene mutations. The reason for this might be PSSM type 2, which is not related to GYS1 mutation. Summerizing, we can say that the high prevalence of the gene mutation responsible for PSSM type 1 has a big impact on the exertional rhabdomyolysis syndromes produced by the affected horses. Except for looking at the genetic background, we have to pay attention to other factors that may contribute to causing the syndromes, such as the levels of Se and vit E, minerals and complex-making ions in the forage, and other causes independent from genetics.